Sound barrier wall

ABSTRACT

A method of forming a monolithically fabricated sound absorbing structural precast concrete noise barrier panel comprising a sound absorbing layer of specialized raw materials. The method includes providing a sound absorbing layer that is a blended mixture of an aggregate, granulated rubber, chemically treated wood particles, cement, pozzolans, water, air entraining admixture, and water reducing mixture; placing the sound absorptive layer ingredients in a form mold; compressing the ingredients to a preset density; backing the compressed ingredients with reinforced structural concrete; and curing the backed and compressed ingredients.

The present application is a divisional of and claims priority to U.S.patent application Ser. No. 12/928,675, filed Dec. 17, 2010, the entirecontents of which are hereby incorporated by reference.

TECHNICAL FIELD OF THE INVENTION Background of the Invention

Since the advent of complex motorized transportation systems, such asrailroads, automobiles and airplanes, there has been a need to reduce orprevent noise caused by such systems from effecting surroundingneighborhoods and businesses. As highways increasingly are compelled totraverse residential areas, hospital zones and even industrial areas inwhich silence is a virtue, a problem arises with respect to the noisegenerated by the vehicles traveling on such highways. The problem isparticularly pronounced as vehicle size increases and vehicle speedincreases both for heavy vehicles and light vehicles.

Not only does the sound generated by traveling vehicles rank as aninconvenience to neighbors of such highways, but there is increasingevidence that continuous high noise levels associated with vehicletravel are detrimental to the health of individuals who dwell or work inthe vicinity of highways, throughways, heavily traveled streets andavenues, and even carparks where both engine starting and wheel noisemay be significant.

As such, in a growing number of transportation related settings,federal, state and local governments are specifying, supplying andinstalling sound barriers between roadways and the surrounding areas,particularly in areas of high traffic volume. Sound barriers aredesirable in residential and commercial areas proximate interstatehighways to attenuate noise in neighborhoods, shopping districts, andother commercial areas caused by traffic.

Therefore, there is a need for a noise barrier wall that has a highnoise reduction coefficient yet also has a high sound transmissioncoefficient. Consequently, a number of devices and systems have beencreated which have been somewhat effective in alternating such noise.

Various materials are presently employed in the design and manufactureof various sound barriers. Prior art barrier designs constructed ofsteel, concrete, cement board, wood, and earthen barriers have beenemployed to effect a reduction of ambient noise levels proximate noisyroadways or construction sites. However, each have various disadvantagesthat make widespread production and installation impractical, either dueto cost, manufacture and installation complexity, or poor soundattenuation.

Common barriers such as fences constructed of wood or a similarlightweight material probably served as the first noise barriers. Whileeffective in preventing sight access, such barriers are quiteineffective in preventing the transmission of sound waves. Steel andmetal barriers are prone to denting and chipping, as well as corrosion,and are extremely heavy. Wood barriers require periodic maintenance andhave a comparatively short useful life. Concrete> barriers are veryexpensive to produce and install. Earthen barriers require a great dealof space to erect and are subject to erosion over time. Furthermore,each of these barrier designs requires labor intensive installationtechniques, thereby placing a premium on product life. Additionally,none of the aforementioned barrier designs are particularlyaesthetically pleasing, and all are susceptible to the application ofgraffiti and the like.

Therefore, there is a need for a sound barrier that is durable.

Concrete or masonry barriers and barriers constructed of a similar heavymaterial are perhaps more commonly used in attempting to prevent noisetransmission. Barriers constructed of concrete are far superior to woodstructures in accomplishing this goal, and yet it has been determinedthat concrete barriers and the like tend more to reflect sound wavesrather than to dampen or absorb the same. Hence, while these types ofbarriers seem to be suitable for the accomplishment of some tasks alonga highway or railroad track, they leave much to be desired in the areaof preventing sound wave from being redirected or reflected onto peopleliving in areas opposite a noise barrier wall installation.

Additionally, the installation of many prior art sound barriers requiresan excess of installation hardware and complex mechanical hardware forassembling the barrier panels. Concrete and steel barriers require heavyequipment to place the barriers, and robust structural supports to holdthe barriers in place due to their weight. Furthermore, the laborrequired to construct these barrier systems is quite costly.

Since many sound barriers are located adjacent to high speed motorways,there is a considerable possibility of impact between the barrier and avehicle that is traveling at high speeds. As such, there is apossibility of damage to the barrier, which can cause considerableexpense to correct. Furthermore, these structures are exposed to theelements, and as such, are susceptible to damage due to hail, as well asto freeze/thaw cycles. Again, repair of such damage can be quiteexpensive.

Therefore, there is a need for a sound barrier that is durable yet iseconomical to construct and erect, as well as to maintain.

Still further, since some of these structures are located nearresidential areas, fire may be a consideration both to protect thestructures themselves as well as to protect nearby structures.

Therefore, there is a need for a sound wall that has a good fire rating.

Lately, much experimentation has been done with barriers having extrudedmembers, particularly those which are modularly connected together, someof which are constructed of thermoplastic materials which absorb ratherthan deflect sound waves. Such structures may be effective in dampeningmuch of the noise generated by highway traffic, locomotives, airplanes,and the like, although these barriers are not as effective as desirable.Furthermore, many of these barriers are constructed of materials whichbreak down quickly or lose their resiliency when subjected to adverseconditions such as extreme weather and high-velocity impacts withforeign objects.

Some sound barriers use large quantities of rubber shavings containedwithin a hollow fiberglass panel in an effort to reduce sound reflectionand/or transmission. However, it has been found that these structuresare vulnerable to damage caused by changing weather conditions andvandalism. This type of barrier becomes a fire hazard in the event avehicle crashes into the wall and spills fuel onto the wall.

Since sound barriers are often used to protect residential areas,hospitals, schools, and housing developments from high noise areas likeroadways, construction sites, and shopping centers, the design andconstruction of economical and easily installed barriers is ofparticular import to quality of life in the modern world. Consequently,aesthetic appeal of such barriers has become a significant element inthe design of such structures.

Therefore, there is a need for a sound wall that can be constructed in amanner that is aesthetically pleasing.

Still further, in any sound wall that has a sound absorbing layer bondedto a structural unit, the bond between the sound absorbing layer and thestructural concrete layer is very critical. If the bond between thesound absorbing layer and the structural concrete layer is weak, thesound absorbing layer can dislodges from the structural concrete layer.Failure of the bond is dangerous because large pieces of the soundabsorbing layer fall and endanger the general public. Consequently, manycomposite sound walls have become expensive and complicated tomanufacture, difficult to erect, and expensive to maintain.

Therefore, there is a need for a sound wall that can be formed ofseveral components, yet will be securely bonded to any structuralelement while still remaining efficient to manufacture, erect andmaintain.

SUMMARY OF THE INVENTION

These, and other objects are achieved by a monolithically fabricatedsound absorbing structural precast panel. One form of the panel iscomprised of a sound absorptive layer that is a blended mixture ofexpanded aggregate or natural aggregate or manmade aggregate, recycledgranulated rubber or granulated rubber, chemically treated woodparticles, cement, pozzolans, water, syntheticpolypropylene/polyethylene Monofilament Fibers (optional), airentraining admixture, water reducing, set acceleration admixtures, setretarding admixtures, super plasticizers admixture. The mixture isplaced in a form mold, compressed to a specific density, backed withreinforced structural concrete and cured. The result is a soundabsorbing structural precast panel that is economical to manufacture,has a high noise reduction coefficient, high sound transmissioncoefficient, above average freeze-thaw durability, above averageresistance to chemical attack and a Class A fire rating. Panelfabrication can be conducted at a manufacturing facility or at aconstruction site. The panel fabrication-placement processes can bepreformed manually or mechanically. If preformed, manually thefabrication process does not require specialized placement tools. Amodified mixture can include recycled HDPVC. Other modified mixtures caninclude water reducing admixtures, set retarding admixtures, setacceleration, super plasticizer admixtures and Syntheticpolypropylene/polyethylene Monofilament Fibers.

The primary use of the sound absorbing noise barrier embodying theprinciples of the present invention is noise abatement for thetransportation industry, such as highway, railway and mass transit.Additionally, the panel provides noise abatement for residential,commercial or industrial applications requiring a durable, low cost,sound absorbing noise barrier.

Other systems, methods, features, and advantages of the invention willbe, or will become, apparent to one with skill in the art uponexamination of the following figures and detailed description. It isintended that all such additional systems, methods, features, andadvantages be included within this description, be within the scope ofthe invention, and be protected by the following claims.

DETAILED DESCRIPTION OF THE INVENTION

The principles of the present invention are embodied in a monolithicallyfabricated composite sound absorbing structural concrete noise barriercomprising a sound absorbing layer formed of specialized raw materialswhich is compressed to a specific density and bonded to a reinforcedstructural concrete layer.

Specifically, the sound absorbing layer is formed as follows (with allvolume being based upon one cubic yard):

Sound absorbing mixture volume based upon 1 cubic yard.

Cement and Pozzolan: 19% to 30% by volume.

Normal weight or Lightweight Aggregate: 16%-23% by volume.

Wood particles: 15% to 22% by volume.

Granulated rubber: 19%-28% by volume.

Potable water: 8%-15% by volume.

Air entraining admixture: 5-40 oz per cubic yard.

Optional Ingredients Include:

Synthetic polypropylene/polyethylene Monofilament Fibers 0.5%-1.5% byvolume.

Water reducing admixtures: 5-15 oz per cubic yard (optional).

Set Retarding Admixture: 5-15 oz per yard (optional).

Super plasticizer admixture: per manufactures dosage rate (optional)

Recycled High Density Polyvinyl Chloride (7% to 20% by volume)

Set Accelerating Admixtures: per manufacture dosage rate (optional)

The advantages associated with the optional ingredients include thefollowing.

Synthetic Polypropylene/Polyethylene Monofilament Fibers:

The advantages of using synthetic polypropylene/polyethylenemonofilament fibers in the Sound absorbing mixture is the maximumacoustic absorption coefficient increases for various frequencies fromaround 0.70 for a mixture with no fibers to around 0.90 for a mixturesfiber volume of 1.5%. The increased acoustical absorption is due to thefibers in the sound absorbing mixture bridging some of the larger pores.When sound waves pass through the open pore structure of the soundabsorbing layer, they impinge on the fibers. Consequently, the path thesound waves travel is increased. A portion of the sound energy is lostin traveling around the fibers and another portion is lost in settingthe fibers into vibration. The sound energy loss due to the interactionof both of these mechanisms is increased, resulting in increasedacoustic absorption.

Water Reducing Admixtures.

Water reducing admixtures reduce the amount of mixing water used in thesound absorbing mixture without sacrificing the mixtures workability. Inaddition, reducing the mixing water results in the sound absorbing layerhaving increased compressive strength, increased flexural strength andimproved freeze-thaw resistance.

Set Retarding Admixtures.

Set retarding admixtures are used when the temperature of the soundabsorbing mixture exceeds 90 Degrees F. As the temperature of the soundabsorbing mixture increases, the chemical hydration process of thecement is accelerated thus causing the mixture to set more rapidly andlose workability. Adding a set retarding admixture delays the cementshydration process and allows the mixture to have the workabilitycharacteristics of a normal mixture.

Super Plasticizers.

Super plasticizers, also known as plasticizers, are admixtures thatallow large water reduction or greater flowability without substantiallyslowing set time. A Super Plasticizer can maintain a specificconsistency and workability at a greatly reduced amount of water. Superplasticizers have a limited pot life and will lose their effectiveness.Dosages rates vary according to the particular brand and type of superplasticizer. When added to the sound absorbing mixture, superplasticizers produce a sound absorbing layer that gains strength fasterthat the standard sound absorbing mixture. Consequently, the timerequired to cure the sound absorbing panels is reduced and the panelscan be removed from the forms in a shorter period of time. This improvesproduction rates.

Unlike a set retarder that extends the setting time of a mixture, asuper plasticizer maintains consistency and workability for a specifictime and does not retard the set time of the sound absorbing admixture.

This is a substantial benefit when placing large quantities of the soundabsorbing mixture quickly in a limited time period.

Recycled High Density Polyvinyl Chloride (HDPVC).

Recycled High Density Polyvinyl Chloride (HDPVC) is an environmentalwaste product that when recycled to a specific gradation and properlysized reduces the weight of the sound absorbing layer and enhances boththe pore structure and interconnected channels within the soundabsorbing layer. When recycled HDPVC is used in the sound absorbingmixture, it replaces an equal volume of stone aggregate. HDPVC may be anenvironmental problem, but large stockpiles are available for usethroughout the world. Currently the demand for recycled HDPVC is lessthat the available supply.

Set Acceleration Admixture.

Set acceleration admixture is used in the sound absorbing mixture whenthe mixture temperature is 40 degrees Fahrenheit or less. At 40 degreesF., the heat from the chemical hydration of the cement and water slows,consequently, the sound absorbing layer's set time increases. Anincrease in set time delays the removal of the noise barrier panels fromtheir forms. To lessen the impact of low mixture temperatures andmaintain production levels, set accelerating admixtures are added to thesound absorbing mixture per the admixture manufactures recommendeddosage rate.

Mixing the Sound Absorbing Mixture.

The sound absorbing mixture can be mixed in many different types ofmotorized mixers. A mixer must have a mixing speed and mixing capacitysufficient in size to completely mix the sound absorbing raw materialsinto a uniform consistency. Examples of different type of mixerssuitable for mixing the sound absorbing mixture are mixers having amixing action comprised of singular or dual rotating horizontal shafts,affixed to each horizontal shaft are arms with paddles that extendvertically into the mixture, or mixers having a rotating vertical shaftwith numerous arms extending outward from the shaft, affixed to each armand at different locations along each arm are paddles extendingvertically into the mixture, or mixers having a horizontal shaft with acontinuous spiral mixing screw attached to the shaft, or a mobile mixingunit capable of discharging the raw material into a screw type mixingauger.

The quantity of each raw material is determined either by weight orvolume. The first raw materials introduced into the mixer are the stoneaggregate, rubber granules, wood particles, fibers and any optionalaggregate; these are mixed for 15-30 seconds. Second, the cement andPozzolans are discharged into the mixer and mixed until uniformlyblended. Third, the water and admixture are discharged into the mixtureat a minimum water discharge rate of 2 gallons per second. The airentraining admixture is discharged into the water discharge line anddischarged as the water is discharging. The remaining admixtures aredischarged after the air entraining admixture has finished discharging.The raw materials are mixed or a minimum of two (2) minutes. At the endof the 2 minute mixing cycle, a check is made that the sound absorbingmixture has the correct consistency and is uniformly blended. If themixture is not uniformly blended, it should be mixed for an additional1-2 minutes.

The present invention is a sound absorbing precast panel consisting of asound absorbing layer comprised of the ingredients listed herein andbonded to a layer of reinforced structural lightweight or normal weightconcrete. A plurality of plastic or metal units support and position thereinforcement at designated heights within the structural layer. Varioussizes of reinforcement mesh or bars comprised of metal or fiber glass orcarbon fiber are placed individually or in combination on the supportingunits. The supporting units rest upon the compacted sound absorbinglayer.

The stone aggregate, granulated rubber particles and chemically treatedwood particles used in the sound absorbing layer of the presentinvention are binary blends of specific sizes. Blending specific sizedstone aggregates, rubber particles and chemically treated wood particlesincreases the porosity of the sound absorbing layer and the durabilityof the product.

Additionally, binary blends of stone aggregate, granulated rubber andchemically treated wood particles increase the number of interconnectedchannels within the sound absorbing layer that sound waves travelthrough. Binary blending of stone aggregate, granulated rubber andchemically treated wood particles also increases the tortuosity withinthe interconnected sound absorbing channels, thus more sound energy isabsorbed.

The increased porosity and increased number of interconnected channelsimproves the durability of the sound absorbing layer. Most soundabsorbing products known to the inventor have difficulty expelling waterquickly from the sound absorbing layer. Thus, many of the existing soundabsorbing noise barriers lack long term durability and deteriorate inclimates that experience numerous free/thaw cycles. The presentinvention binary blending of stone aggregate, granulated rubber andchemically treated wood particles increases the porosity and the numberof interconnected channels; consequently moisture or water within thesound absorbing layer is expelled from the sound absorbing layer at rateof 21 gallons per minute. This represents a 40% increase in the amountmoisture expelled from similar sound absorbing products. The fasterwater is expelled from a sound absorbing layer the less opportunitymoisture has to freeze and expand within the pores and interconnectedchannels of the sound absorbing layer. Moisture that is trapped withinthe sound absorbing layer freezes and is the primary reason soundabsorbing noise barriers deteriorate. As the moisture freezes, excessiveinternal pressure may be created which may cause the sound absorbingmass to break apart and fail when undergoing numerous freeze-thawcycles. The product embodying the teaching of the present invention hasbeen tested per ASTM Standard 666, Method A (Method for testing theFreeze-Thaw resistance of concrete) and has exhibited excellentfree-thaw resistance.

The natural aggregate, expanded aggregate, man-made aggregate,lightweight aggregate, granulated rubber and wood particles are binaryblends of specific sizes designed to create a void content within thesound absorbing layer that ranges between 15% to 38% voids. The voidcontent is enhanced and optimized by controlling the gradation, the sizeand the quantity of the various aggregates, granulated rubber,chemically treated wood particles and optional recycles HDPVC.

The product of the present invention uses chemically treated woodparticles to replace a percentage of the stone aggregate. One advantageof replacing the stone aggregate with chemically treated wood particlesis the weight of the sound absorbing panel decreases. Stone aggregateweights can range from an average weight of about 45 lbs per cubic footfor lightweight aggregate to an aggregate weight of about 100 lbs percubic foot for regular aggregate. Wood particles weigh about 10 lbs percubic foot. In one (1) cubic yard of sound absorbing mixture, so thechemically treated wood particles can replace 4 to 6 cubic foot of stoneaggregate. Depending upon the type of stone aggregate that is replacedwith wood fiber the weight reduction can be from 180 lbs to 600 lbs percubic yard. An 8′×20′ panel requires 2 cubic yards of sound absorbingmixture this could reduce the weight 360 lbs to 1200 lbs per panel.

Using wood granules or fibers in the sound absorbing mixture enables themanufacturer to cast noise barrier panels having a very detailed soundabsorbing surface. Wood chips are flexible and can bend and conform tothe detail of a formliner. As used herein, formliner detail is thepattern of a premolded formliner replicating a look of brick, block,stone or a ribbed pattern, etc. Each pattern has its own unique corners,edges and irregularities. The sound absorbing mixture must be able toconform to and recreate the pattern. Due to the flexibility of the woodgranules, more definition and detail can be achieved with the additionof wood granules than with a mixture of granulated rubber and stoneaggregate. As used herein, a formliner is a rubber, or plastic linerthat is placed at the bottom of the form and creates the face of apanel.

Another advantage of using chemically treated wood particles is thatunlike stone aggregate and granulated rubber, wood particles arefibrous. The fibrous nature of wood makes wood particles natural soundabsorbers. A stone aggregate and granulated rubber mixture createschannels that dissipates sound energy and absorb noise. However, thestone aggregate also reflects noise. Replacing a percentage of stoneaggregate with chemically treated wood particles decreases the amount ofreflected sound energy and increased sound absorption. An additionaladvantage of using chemically treated wood particles is the woodparticles create additional tortuosity within the interconnected soundabsorbing channels. Increasing the tortuosity within the interconnectedsound absorbing channels dissipates additional sound energy.Consequently, using chemically treated wood particles in the soundabsorbing layer increases the amount of absorbed sound energy.

As mentioned above, the bond between the sound absorbing layer and thestructural concrete layer is very critical. If the bond between thelayers is weak the sound absorbing layer can dislodges from thestructural concrete layer. Failure of the bond is dangerous becauselarge pieces of the sound absorbing layer may fall and endanger thegeneral public.

Products using a cement binder mixed with only chemically treated woodparticles to create a sound absorbing layer must place the structuralconcrete onto the sound absorbing layer before the sound absorbinglayers cement hydrates. This is because the chemical reaction of thesound absorbing layers cement and the structural concrete layers cementmust hydrate together to create a strong bond between the layers. If thetime between of the sound absorbing layer and placement of thestructural concrete is delayed due to a plant break down or fabricationproblem the sound absorbing layer will hydrate before placement of thestructural layer. Consequently, the bond between the layers will lackstrength. To avoid this problem, some government agencies have requiredsound absorbing panels manufactured with only chemically treated woodparticles and a cement binder to insert stainless steel connectors thatextend into the sound absorbing layer and into the structural concretelayer. The stainless steel connector acts as a secondary way to bondeach layer together should the chemically bond be inferior or fail.

The primary bond between the sound absorbing layer of the productembodying the present invention and the structural concrete layer usesthe porosity of the sound absorbing layer to securely bond each layertogether. Due to the large number of ⅛″ to ¼″ sized pores distributedacross the entire sound absorbing layer a strong bond is created whenthe structural concrete is placed upon the sound absorbing layer.

This type of bond is not dependent upon the chemical hydration of thecement and water in each layer to bond the layers together.Consequently, the structural concrete layer can be placed upon the soundabsorbing layer a day, week, or month later and the panel manufacturercan be assured the bonding of the two layers is strong. Additionally,since the bond between the layers of the present invention is not timecritical, the sound absorbing noise barrier panels do not have to bemanufactured in a controlled environment. Panels can be manufacturedindoors or outdoors or at a construction site.

Furthermore, the sound absorbing layer of the present invention can beplaced manually using simple, low cost, readily-available tools.Expensive specialized placement equipment is not required to manufacturesound absorbing noise barriers, thereby making small sound absorbingnoise barrier projects economical to manufacture. The present inventionmay enable more manufactures to manufacture sound absorbing noisebarriers. This may stimulate competition and thereby reduce the cost ofsound absorbing noise barriers.

Forming.

The present invention is fabricated in forms that are sized according toeach sound absorbing panel's depth, length and width as indicated by thejob specifications of the project being manufactured. The forms includea plurality of perimeter side forms, supporting base form, bulkheads andhardware used to secure the perimeter side form, bulkheads, and baseforms together. The perimeter side forms are constructed of strong,ridged, non bending materials. Examples of perimeter side form materialsare steel, wood, fiberglass, etc. The side forms are placed upon aridged non-bending base designed to support the weight of the loadsimposed upon the base throughout the fabricating process. The perimeterside forms are configured to the correct dimensions and secured to thebase form using removable attaching hardware. If a formliner design isrequired, a formliner is placed inside the perimeter form work on top ofthe base form. After the formliner is in place, the inside area of theform assembly is lightly spray with an approved form release chemical.The form assemblies are then complete.

Because the present invention's sound absorbing surface has an abundanceof pores, formliners do not need to be secured permanently to the baseform. Normally if a formliner is not permanently secured to the baseform when the sound absorbing panel is removed from the form, thesuction created between the formliner and the sound absorbing surfacepulls the formliner from the base form and causes it to stick to thesound absorbing surface. The advantage of securing the formliner to thebase form is that different formliners can be installed onto the baseform quickly without losing valuable production time. Another advantageof the present invention is it reduces formliner cost.

Formliners are expensive and have limited useful lives. Because of thepresent invention's increased surface porosity, the number of times aformliner can be used is increased. Using the teaching of the presentinvention, the useful life of a formliner can be increased from twohundred to four hundred uses. This represents a large cost saving whenconsidering the average formliner cost ranges from $22.00-$36.00 asquare foot.

It is noted that an additional advantage to the present invention isrealized in some geographic regions where locating correctly sized andgraded lightweight aggregate is difficult. In these situation thelightweight aggregate may have to be used. Consequently, using this typeof lightweight aggregate decreases the interconnected void structurewithin the sound absorbing mass. To offset the decrease in voids andrestore the interconnected void structure to the proper content,additional quantities of wood particles may be added to the soundabsorbing mixture. Blending the extra wood particles with thelightweight aggregate creates additional voids and restores the interconnected voids content to the volume of voids needed for efficientsound absorption.

While various embodiments of the invention have been described, it willbe apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible within the scope of thisinvention. Accordingly, the invention is not to be restricted except inlight of the attached claims and their equivalents.

1. A method of forming a monolithic sound absorbing structural precastpanel comprising: A) providing a sound absorptive layer that is ablended mixture wherein the blended mixture is selected from the groupconsisting of expanded aggregate, natural aggregate, and manmadeaggregate; the mixture further including granulated rubber, chemicallytreated wood particles, cement, pozzolans, water, air entrainingadmixture, and water reducing mixture; B) placing the sound absorptivelayer ingredients in a form mold; C) compressing the ingredients to apreset density; D) backing the compressed ingredients with reinforcedstructural concrete; and E) curing the backed and compressedingredients.